MLAT tracks breaking

For some reason even though aircraft are high and well within my receiver range, some MLAT tracks will break, is this a problem with my MLAT client or something else?

I have added an example below

I suspect your track is blocked by some obstruction in the line of sight between the antenna and the aircraft.
The dotted track is the estimated track between the 2 last known measurement points.
It could be a building, a tree or any other form of obstruction.

I can track adsb aircraft through the same area without issues, that was just one example of mlat tracks which break yesterday or maybe Sunday I had an eastern airways go right over me and the track was lost for probably 40 miles

You could add the RSSI (Signal strength) to the view so you can see how “loud” the signal is from that particular aicraft. It might be overloading the reciever at that point in time.

I have some adaptive commands running to counter such issues

Just as a matter of interest, why isn’t a commercial airliner flying at 27,000 feet transmitting ADSB signals?

In my part of the world (and I assume in the UK) that is mandatory.

It’s not mandatory as yet in the UK or Europe

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The problem could be that there are not enough other receivers to be able to MLAT that area.
4 receivers are required but I suppose it could be that there isn’t enough overlapping coverage with your receiver to maintain the required number.

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The lack of receivers is unlikely to be the issue as it happens directly over me in a populated area where a large number of feeders are syncing

Looking at the FA online track for that aircraft at 1636 UTC, the time of your online local screen capture, there were plenty of good mlat results. The online track shows several mlat results every minute for the past 10 minutes.

That tells me that FA calculated good mlat positions, but did NOT send them to you. I believe FA only returns mlat results to you that you contribute to, and then continues with mlat results for a certain amount of time after that.

This is just a guess, but perhaps FA selectively chooses not to include your station in the mlat calculations of aircraft very close, or directly overhead your position. Mlat curves right overhead would probably be unusable anyway, so FA might just choose to ignore your data for that period of time. Then, since the software thinks you are “no longer contributing to the mlat calculations”, it decides not to send you the mlat results.

Pure speculation, but that might explain it.

If true, FA might wish to continue sending mlat data to stations deselected for this reason. They might not be contributing, but should probably still benefit from the results.


This is what the grace period is for, where we continue to send results for a while even when not using the receiver data.

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Another example here cruising at 36,000ft but again a large gap in the tracking on mlat

But virtually the same area and almost 50% lower on adsb and tracking is no bother

You’re more likely to get selected for a lower-flying aircraft because fewer receivers can see it.

Your part of the world is extremely well covered. There might be a few thousand receivers that can see that aircraft at FL360.

What confuses me somewhat is as per yesterday’s example I lose a track on a 27,000ft mlat but just now I’m tracking a USAF tanker over the same area at a lower altitude to that which dropped out a short time ago and only slightly higher than earlier this morning, yet it held throughout


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